#define _CRT_SECURE_NO_WARNINGS 1
#include<stdio.h>
int main()
{
	int n = 0;
	int num = 0;
	int ret =  0;
	int i = 0;
	scanf("%d",&n);
	for(i=0;i<n;i++)
	{
	    scanf("%d",&num);
		ret ^= num;
	}
	printf("%d\n",ret);
    return 0;
}